Microbial conversion of agro-industrial residues to surfactin: a review of fermentation performance, process optimization, product recovery and agricultural applications

Surfactin, a lipopeptide biosurfactant, has drawn growing attention for agricultural use, but its large-scale production remains limited by substrate cost, low titers, and downstream recovery. This review compiles quantitative data on agro-industrial residues as feedstocks, comparing substrate classes, fermentation performance, optimization routes, recovery methods, and field-level applications reported to date, drawing mainly on Scopus-indexed literature published in 2016–2026 together with earlier key studies. Across different agro-industrial waste-valorization based systems, submerged fermentation produced a titer range of 0.0265-4.8 g L -1 , whereas solid-state processes showed yields of 2.0-6.25 g kg -1 across residue types. Although these values are expressed on different bases and are not directly comparable, they remain below the 12.8–52.6 g L -1 reported for engineered strains grown on defined media. Furthermore, not all reported yields were confirmed as surfactin through chromatographic analysis. Statistical and computational optimization and foam-based downstream product recovery improved titers and product enrichment, but only at laboratory scale. Agricultural effects, including biocontrol and nematocidal activity, have been shown mainly with purified surfactin, crude lipopeptide extracts or living Bacillus strains, and rarely with waste-derived material. Matched comparisons of waste-derived and defined-medium surfactin in plant systems are still lacking, and recovery data beyond laboratory scale remain scarce. Overall, the literature indicates that substrate selection, strain–substrate matching, process optimization, and recovery efficiency are the main factors that will determine whether laboratory-scale waste valorization can progress to agricultural application.